A variety of concepts for constructing high-pressure sensors having a sensor element and a connector piece are known from practical use.
These two components are usually fabricated independently of one another from a metallic base element. In the case of the sensor element, the base element is equipped with a blind opening in order to expose a diaphragm in the oppositely located surface of the base element. Circuit elements for signal acquisition are disposed on this surface, semiconductor technology methods being used, for example, for this purpose. A pressure conduit is embodied in the base element of the connector piece. In addition, the connector piece can also be equipped, for example, with a thread for coupling to the system to be measured. The sensor element is then mounted on the connector piece in such a way that the rearward blind opening of the sensor element is disposed in alignment with the pressure conduit in the connector piece.
This mounting of the sensor element on the connector piece proves to be problematic in practical use.
For cost reasons, the sensor element is usually welded to the connector piece. Care must be taken in this context that neither the pressure conduit in the connector piece nor the blind opening of the sensor element becomes sealed off, contaminated, or unfavorably deformed; this complicates production of a welded connection having reproducible mechanical properties. The compressive strength of the welded connection is influenced by the geometry of the weld bead and of the contact surfaces with respect to the sensor element and the connector piece. Notches or depressions in the welded connection constitute initiation points for cracks under high pressure loads, in particular in the case of pulsating loads. The field of application of such high-pressure sensors is therefore typically limited to pressure ranges below 2200 bar.
Clamped connections are more reliable than a welded connection between the sensor element and connector piece. They are suitable even for use at pressures greater than 10,000 bar. The costs associated therewith are, however, very high, so that this construction and connection technology is utilized only in very small production runs for special applications.
The sensor element and the connector piece can also be produced in one piece from a metallic base element. In this case, however, because of the component size, the circuit elements for signal acquisition cannot readily be applied onto the sensor diaphragm using semiconductor technology methods.